1. Field of the Invention
The present invention relates to an inkjet recording apparatus, and more particularly to image recording (forming) technology for recording (forming) an image on a recording medium by reacting ink with a treatment liquid to fix the ink onto the recording medium.
2. Description of the Related Art
In recent years, inkjet recording apparatuses have come to be used widely as data output apparatuses for outputting images, documents, or the like. By driving recording elements, such as nozzles, provided in a recording head in accordance with data, an inkjet recording apparatus is able to form an image, document, or the like, corresponding to data, onto a recording medium, by means of ink ejected from the nozzles.
In an inkjet recording apparatus, in order to improve the quality of the printed image, the dot size and the dot pitch are decided in such a manner that micro-size dots are formed at high density on the medium, and mutually adjacent dots overlap with each other in an image formed by dots at high density. Moreover, in a color image, ink droplets of a plurality of colors are successively superimposed on each other before becoming fixed in the medium. When a plurality of dots are mutually superimposed on each other in this way, there may be occurrence of density non-uniformities, or bleeding (between colors), or the like, due to landing interference in which ink droplets combine together during landing onto the medium. Non-uniformity and bleeding of this kind may cause a notable decline in the quality of the printed image, and may make it impossible to obtain a satisfactory (desired) image.
In order to obtain a desirable image without a decline in the quality of the printed image, a method is proposed that coloring materials (ink substrates) contained in the ink is fixed onto the medium (or the coloring materials agglutinate together) by ejecting ink droplets after a treatment liquid comprising a cationic polymer (polyallylamine, polyamine sulfone, polyvinylamine, chitosan, and neutralized products thereof), or an anionic polymer (polyacrylate, shellac, styrene-acrylate copolymer, styrene-maleic anhydride copolymer, or the like) is deposited on the medium, thereby preventing bleeding or landing interference of the ink.
In an image forming apparatus and an image forming method which are described in Japanese Patent Application Publication No.9-193367, in order to shorten the time period from the application of treatment liquid until the ejection of ink droplets, a coating roller for applying the treatment liquid in a contactable condition toward the recording medium prior to ink ejection is provided in the carriage for moving the inkjet recording head relatively with respect to the recording medium.
Furthermore, in an inkjet recording apparatus described in Japanese Patent Application Publication No. 8-72234,a plurality of recording heads are provided for capable of ejecting ink and treatment liquid independently, and the heads for ejecting droplets of treatment liquid are provided at the respective ends of the heads for ejecting ink so that the ejection of treatment liquid is always performed before the ejection of ink, and the time period from the ejection of droplets of treatment liquid until the ejection of droplets of ink is shortened.
Generally, in order to deposit treatment liquid onto a recording medium, there is a method in which treatment liquid is applied to an entire surface by means of a coating roller or the like, and a method in which droplets of treatment liquid are ejected by means of a print head (ejection), similarly to ink. However, in the method in which the treatment liquid is applied by using a coating roller or the like, since the treatment liquid is applied to regions where ink droplets are not to be ejected, the treatment liquid remains on the medium even after printing has completed (after the end of droplet ejection), and then the burden of solvent processing for removing the surplus treatment liquid, and the like, is increased. In particular, when using a non-permeable medium, such the problem is notable.
On the other hand, in the method in which droplets of treatment liquid are ejected by using a print head, especially in the case of using a permeable type of medium, when the droplets of ink are ejected from a head positioned further downstream, the treatment liquid have already permeated into the medium. Therefore, a reaction between the ink and the treatment liquid may not be achieved.
In the technologies which are disclosed with respect to the image forming apparatus and image forming method described in Japanese Patent Application Publication No. 9-193367 and the inkjet recording apparatus described in Japanese Patent Application Publication No. 8-72234,it is not sufficient to resolve the various problems that may occur depending on conditions such as the type of medium, the image contents, the ink droplet ejection volume, and the like.